The present invention relates to fuel ignition systems, and particularly to such systems for forming electrical field discharges at the flame front of burning hydrocarbon fuels, particularly in internal combustion engines.
Considerable research has been conducted on ignition systems and on fuels for internal combustion engines with the objective of improving the combustion of the air-fuel mixture. More specifically, during the past thirty years there has been work done on improving the ability of ignition systems for igniting the fuel, especially of the inherently cleaner and more efficiently burning lean air-fuel mixtures, and also for improving the anti-knock characteristics of the fuel itself so that higher engine compression ratios can be used for higher internal combustion engine efficiency.
The prior art work on ignition has focussed on improving the ignition voltage and the spark's energy content, and on sustaining high electromagnetic (EM) fields at the flame front. Little attention, however, appears to have been given to actually improving the electrical coupling to the flame front, and to using the hydrocarbon air-fuel flame front plasma as a source of ignition plasma for absorbing electrical (discharge) energy.
Prior work on hydrocarbon fuels appears to have been largely limited to work on improving the fuel's anti-knock characteristic or octane rating and on the fuel's volatility. Little or no attention seems to have been given towards using the fuel's combustion plasma generating properties (or plasma rating as described hereinafter) as an approach for improving the ignition and combustion. The limited work on fuels appears to have occurred because, with few exceptions, no practical proposals were made to use the fuel's flame plasma generating properties in the internal combustion engine to electrically stimulate the combustion to improve lean mixture combustion.
Prior art work on spark ignition aspects are numerous, and for example, are summarized in Edward F. Obert's book, "Internal Combustion Engines and Air Pollution", pp. 532 to 566, Spark-Ignition Engines, Intext Educational Publishers, 1973. The work reported by Obert, and most the work since then, does not discuss the plasma properties of the flame. Earlier work by the applicant herein has been limited principally to the very high frequency (microwave) coupling to the flame plasma. For example, work on generating and maintaining a high electromagnetic field in the combustion chamber is disclosed in U.S. Pat. Nos. 3,934,566 and 4,138,980, where the concept of electromagnetically stimulated combustion is introduced. In these cases, EM stimulation can be made to occur in the entire combustion volume by high frequency electric fields resonantly stored in the combustion chamber with field strengths of order of 1000 volts/cm/atmosphere, exciting intermediate molecular levels at the flame front plasma. Other prior art of the applicant herein is disclosed in U.S. patent application Ser. No. 885,961, now U.S. Pat. No. 4,774,914 based on U.S. patent application Ser. No. 779,790, where EM flame-front stimulaion occurs near the spark plug site by means of a system designated as "EM Ignition".
In all these cases, while the concept of interacting with the flame plasma is either important or helpful, there is actually no discussion of redesigning the "ignition" system to either enhance or maximize to whatever extent flame discharge ignition naturally occurs, or to force the flame front to become an electrical discharge path for the ignition spark circuit. The closest prior art known is that of the applicant herein, namely the above referenced EM Ignition, wherein EM flame-front stimulation occurs by using a large antenna type plug tip which couples to the flame front: (1) the pre-breakdown electric fields associated with the high voltage rise of secondary pulses, and (2) the high frequency (of MHertz range) EM fields at the spark plug site arising from grounding the spark to the piston face. These electrical fields persist for up to a few microseconds (usecs). In neither case is the present invention contemplated.
Moreover, careful inspection of the antenna type plug tips of the EM Ignition system disclosed show insulator ends which are generally converging and metallic end tips which are either pointed or surrounded at the sides by insulating material. Such structures are of opposing shape to that of the present invention, and furthermore product electric field lines which are bowed outwards from the spark plug end, significantly reducing the electric field intensity from that which is disclosed with reference to the present invention.
Furthermore, in the previous cited cases, and in all the prior art work known to the applicant, there is no discussion of modifying the fuel itself to improve its flame plasma properties for preferentially absorbing electrical energy at the flame front.
A large amount of prior art work on the fuel was largely concerned with the use of lead to increase the octane rating, and is incidently related prior art in that lead reduces the electron-ion recombination coefficient to sustain a higher density plasma at the post-combustion zone or "tail" region of the flame profile which is detrimental to the present invention. Similarly, addition of alkali earth metals (with low ionization potential) to the fuel does produce a large volume, high density plasma during ignition, but since the plasma is generated principally by heating of the fuel, the density profile of the plasma follows the flame temperature profile, once again producing the main plasma in the tail region of the flame.
Other related prior art work is in the area of continuous flowing plasma jet ignitors, for example by Hilliard and Weinberg, Nature 259 (1976), where additional fuel is fed to a plasma jet cavity to feed chemical energy to the plasma by the locally rich burning flame. Such systems are of the dual fuel type with all the associated problems of handling of two fuels.